ࡱ > J L I ` bjbjss 4> H H H H $ L 2 f h h h h h h $ h ! R H H d H 8 f f v pIj S 0 , ! o ! ! { D H H H H H H Material Designation and Numbering Systems
Steel
Steel is composed mainly of iron and carbon with other elements added to create alloys
The AISI-SAE numbering system is very widely used
Hardness(Steel Designation System
In this system a certain alloy is designated with a 4 digit number
The first two numbers specify the alloying elements
The last two numbers specify the carbon content of the steel in hundredths of a percent
Aluminum
AISI system is again widely used
Hardness(Aluminum Designation System
A 4 digit number is used for a wrought alloy
A 3 digit number is used for a casting alloy
The first digit tells what the major alloying elements are
Temper Designation
An additional letter and number attached to the end of the number
Tells how the material has been heat treated
What is hardness testing and why is it important?
Hardness testing is not covered in IDE 110
Can someone give an everyday definition for hardness?
Hardness is defined as The ability to resist permanent indentation
Hardness values alone tell us nothing unless we know what testing method was used
Advantages of hardness testing
Fast
Inexpensive
Nondestructive
If testing is performed properly using the correct method/indenter for a given material
Can be done on a variety of materials if correct test is selected (Dont want this to become destructive testing)
Use of material hardness information
Can be used to approximate the tensile strength of a material
Gives information about the materials resistance to surface wear and abrasion
Types of Hardness Tests
Most hardness tests involve indenting the surface of a material with an indenter
Hardness(Techniques and Equipment(Brinell
Indenter shapes and materials
Ball, cone, pyramid
Hardened steel, diamond, carbide
Indenter size determines scale of the test
We will do macro scale hardness testing
A given load is applied for a prescribed amount of time using a specified indenter and then a measurement is made
Some testing machines require manual measurement of indention (Brinell)
Others will give a direct reading of hardness number from a gage (Rockwell)
Demonstrate some of the different testing devices on hand
Lab Procedure
Each group member will perform the following tests
Brinell test on metal specimen
Rockwell test on metal specimen
Polymer hardness test
Only select materials that have a reference value given on the data sheet for the test you want to perform
Have a reason behind your selection of materials
Brinell Test
We will perform the Brinell test using a 3000 kg load and a 10 mm hardened steel ball indenter
Commonly used on:
Cast iron
Steel
Smaller loads are used on softer materials when performing Brinell tests
Each person will perform one Brinell hardness test on a metal specimen
Select a location at least 2.5 times the indention diameter away from an edge of the specimen or the edge of an indention from a previous test
I will show you how to use the machine once were in the lab
After running the test you will measure the diameter of the indention using a microscope
Take two measurements 90 apart and average them
The reading you get from the microscope will be in mm
If indention is too large to read with microscope you will have to use calipers to measure the diameter
Use the chart on the machine (or formula) to find the Brinell Hardness number (HB)
Formula will likely be needed if you test a copper specimen
Remember that the calipers measure in inches and the formula and chart use millimeters
Next you will estimate the tensile strength
Chart located on wall or ASTM E140 available on the IDE 120 website
Dont need to interpolate unless you want to
Rockwell B/C Test
The Rockwell B test uses a 1/16 diameter steel ball indenter
Rockwell C test uses a diamond cone indenter
Two loads are applied during the test
Minor load of 10 kg applied first
Major load of 100 kg applied after minor
Each person will do three Rockwell tests on your specimen
Distance between any two indentions should be 3 times the indention diameter
Center of all indentions must be at least 2.5 times the indention diameter away from the edge of the specimen
I will show the test method in the lab
The machine will give a direct reading for the Rockwell B/C hardness
Record the hardness as XX HRB on your data sheet
Find the average
If the HRB is above 100 you should use the HRC test
If using a cylindrical specimen you need to apply a correction factor to the value given by the machine
Correction factors can be found from the chart on the wall or Tables 11 and 12 in ASTM E18
Use the wall chart to estimate tensile strength based on the average Rockwell hardness
Polymer Test
There are several choices of tests to perform on the polymers
First select a polymer and then perform a test that has a reference value given on the data sheet
Procedure to follow will vary depending on the test you perform
Will need to perform three tests on your specimen
Then average the three hardness values to find the hardness value you will report
Do not need to estimate tensile strength of the polymer you test
Assignment
Formal report worth 100 points
Summarize what your group was trying to determine when selecting your materials
Create a table showing your results
Compare your hardness and tensile strength results with the reference values
Reference values are provided on the data sheet
Use % error
If a range of reference values is given, find the average and use as the reference value
There will be no % error comparison for the tensile strength of the polymer since you will not have an experimental value for it
Example of table
Material Exp. Hardness Ref. Hardness % Diff. HardnessExp. Tensile Strength (ksi)Ref. Tensile Strength (ksi)% Diff. Tensile Strength
Attach initialed data sheet from lab to memo
Discuss how well your experimental values match the reference values
Give reasons for any major differences
Describe one situation where you would rather use a Brinell hardness test and a different situation where you would prefer to use a Rockwell hardness test
Presentation
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